Ordinary binders that are widely used as binding hardeners of minerals in civil engineering works and construction sites contain limestone, clay, silica, etc. However, it is known that those are sometimes harmful to humans because toxicity remains even after construction, and components from the binders can cause various diseases such as atopy. In addition, civil engineering and construction wastes are common causes for environmental pollution these days. In order to remediate these problems, bio-binders using microbes, particularly, bacteria that can produce urease are described in this invention.
Bacteria, producing urease, have primarily been used to mediate the surface or the base of permeable materials. That is, bacteria have been used to treat oil or petroleum based pollutants, since the fluid velocity decreases as the permeability and porosity of permeable materials are reduced by the bacteria. On the other hand, the bio-binder based on urease-producing bacteria reduces the permeability and porosity through the formation of ammonia, a product of urea decomposition by urease. However, the existing bio-binders do not have enough strength to be used as materials for civil engineering structures and residential buildings.
Meanwhile, more than one third of the entire land on the earth is infertile arid land where trees and plants can hardly grow due to a little rainfall and a lot of evaporation. Also, the area of arid land is gradually expanding and desertification is a major reason for the expansion of arid land. In climatology, arid land means an area where precipitation is less than potential evapotranspiration. The potential evapotranspiration is the sum of evaporation from plants and evaporation from the ground when water is sufficiently supplied to the green area.
Desert soil representing arid land consists mostly of sand whose main components are silica and alumina. The binding strength of the soil is weak because of the inherent nature of sand, so desert soil presents too low strength to be used for road construction, and plants can hardly grow, since it can't retain enough water. In addition, topographical changes are severe because desert wind shifts sand and sandy dust phenomena become more and more frequent. Although attempts have been made in the past to improve the soil strength and wind resistance using microbe-based bio-binders, the strength and the resulting resistance against wind have not been sufficient enough for the binders to be applied to desert environment.